Various types of humidifiers are used to provide moisture to indoor air. Included among such humidifiers are steam humidifiers, ultrasonic humidifiers, porous medium humidifiers and evaporative humidifiers. Many humidifiers employ a removable water storage tank, which can be removed for filling. Typically, a bottom wall of the storage tank is provided with a valve assembly that regulates water flow to maintain a desired water level in a reservoir supplying a humidification device.
Steam humidifiers include a water storage tank and an electric heating element submerged in water to generate steam. Safety devices are provided for switching off the current as soon as the water level drops below the heating element. A flow of hot steam is blown directly into the room to be humidified. As the steam is hot, it may pose a danger to people who come into contact with the steam, or who accidentally overturn the container of hot water. Moreover, in order for the steam to be generated the water must first be boiled. This process may take time and the user may not know whether the device is working, while they wait for steam to be generated.
Ultrasonic humidifiers generally include a container filled with water that is brought to vibration by a high-frequency vibrator, which causes the water to be atomized. An air stream directed onto the water surface carries the mist into the room to be humidified. As the water is not boiled, ultrasonic humidifiers are susceptible to the growth of microorganisms, which may be subsequently carried by the air stream into the room being humidified.
Porous medium humidifiers generally include a porous medium structure partly submerged in cold water in an open vessel and a blower unit drawing air through the porous medium structure. The porous medium may be in the shape of a disc, a drum or a rectangle with part of the medium dipped into the water, which is slowly rotated while air is blown through the portion of the medium above the water level, thus carrying humidity into the room. The porous medium may also be in the form of a stationary body adapted to draw water into the upper non-immersed part by capillary action, it is then carried into the room by air blown therethrough. As the water is not boiled, this method can also lead to the growth of microorganisms, which may be subsequently carried by the air stream into the room being humidified.
Warm-air humidifiers include a container with water, a heated evaporation chamber and a fan adapted for dispersing the generated steam into the room via a passageway. Warm-air humidifiers forestall the growth of bacteria, because the water is heated to the boiling point, but avoid hot steam entering the room by mixing the steam with air which forms a mist, the temperature of which may be determined by the steam to air ratio. However, in order for the steam to be generated the water must be boiled. Because boiling must occur, this method may take time and the user may not know whether the device is working. This type of humidifier may also be complex and expensive.